About Me

I am the former General Counsel of both the Air Force and the United States Army, and a former elected official. I have two blogs--A Guy in the Pew (focused on matters of faith, with some politics and science thrown in for good measure, and A Guy in the World (focused on national security issues). I hope you enjoy both.

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Friday, February 22, 2008

Two very recent studies of genetic diversity have some very interesting implications.

First, a University of Michigan team has announced to results of the largest and most detailed worldwide study of human genetic variation, which offers new insights into early migrations out of Africa and across the globe. Here are highlights from that study:

The latest study characterizes more than 500,000 DNA markers in the human genome and examines variations across 29 populations on five continents.

"Our study is one of the first in a new wave of extremely high-resolution genome scans of population genetic variation," said Rosenberg, an assistant research professor at U-M's Life Sciences Institute and co-senior author of the study, to be published in the Feb. 21 edition of Nature.

"Now that we have the technology to look at thousands, or even hundreds of thousands, of genetic markers, we can infer human population relationships and ancient migrations at a finer level of resolution than has previously been possible."

The new study, led by Rosenberg and National Institute on Aging colleague Andrew Singleton, produced genetic data nearly 100 times more detailed than previous worldwide assessments of human populations.

Among the findings are that genetic diversity is far greater in Africa than in Europe, which offers strong evidence of the "Out-of-Africa"theory--that humans originated in Africa and then migrated around the globe:

Human genetic diversity decreases as distance from Africa—the cradle of humanity—increases. People of African descent are more genetically diverse than Middle Easterners, who are more diverse than Asians and Europeans. Native Americans possess the least-diverse genomes. As a result, searching for disease-causing genes should require the fewest number of genetic markers among Native Americans and the greatest number of markers among Africans.

. . .

The patterns revealed by the new study support the idea that humans originated in Africa, then spread into the Middle East, followed by Europe and Asia, the Pacific Islands, and finally to the Americas.

The results also bolster the notion of "serial founder effects," meaning that as people began migrating eastward from East Africa about 100,000 years ago, each successive wave of migrants carried a subset of the genetic variation held by previous groups.

The second study, done by Cornell scientists, focuses on Eurpoean gentic diversity and it confirms that there is less genetic diversity among those of European dissent:

Human migration from Africa to Europe more than 30,000 years ago appears to have left a mark on the genes of Europeans today.

A Cornell-led study, reported in the Feb. 21 issue of the journal Nature, compared more than 10,000 sequenced genes from 15 African-Americans and 20 European-Americans. The results suggest that European populations have proportionately more harmful variations, though it is unclear what effects these variations actually may have on the overall health of Europeans.

Computer simulations suggest that the first Europeans comprised small and less diverse populations. That would have allowed mildly harmful genetic variations within those populations to become more frequent over time, the researchers report.

"What we may be seeing is a 'population genetic echo' of the founding of Europe," said Carlos Bustamante, assistant professor of biological statistics and computational biology at Cornell and senior co-author with Andrew Clark, a professor of molecular biology and genetics.

"Since we tend to think of European populations as quite large, we did not expect to see a significant difference in the distribution of neutral and deleterious variation between the two populations," said Bustamante. "It was quite surprising, but when we cross-checked our results to data sets gathered by other groups, we found the same trend."